The villains in the expanded Secret Society include: Atomic Skull (Joe Morton), Bizarro, Black Mass, Blockbuster, Cheetah, Copperhead, Devil Ray, Dr. Cyber, Dr. Destiny, Evil Star, Gentlemen Ghost, Giganta, Heatwave, Key, KGBeast, Killer Frost, Major Disaster, Metallo, Parasite, Puzzler, Queen Bee, Rampage, Silver Banshee, Sinestro, Sonar, Star Sapphire, The Shark, The Thinker, Toyman, Volcana, and Weather Wizard.
In addition to referring to Mark 5:9 in The Bible ("And he asked him, What is thy name? And he answered, saying, I am Legion: for we are many"), the title also references the fact that the expanded Secret Society was originally supposed to be called Legion of Doom. They are never actually referred to this in the show because allegedly DC comics instructed the writers not to use the name. The working title was "We Are Legion".
The Justice League runs through the Blackhawk Museum where Killer Shark's, Queen Killer Shark's, King Condor's, The Hoopster's, the 1950s, '60s, and '70s versions of Blackhawk's, Chop Chop's, and Lady Blackhawk's costumes can be seen.
The robot that attacks Lex Luthor, The Key, and Dr. Polaris is resemblence to the Iron Giant (1999).
The spear of Longinus Luther steals from the island is the spear that pierced the side of Jesus on the cross. As Grodd mentions, Adolf Hitler, among other people throughout history, have been interested in acquiring it for its supposed power.